In many surgical procedures, particularly orthopedic procedures, it is common practice to affix a prosthesis to a bone or joint structure for improving the strength, rigidity and movement of the bone/joint structure. Such prosthetic devices have been widely used, hip joints and knee joints are the most common examples of areas where prosthetic devices are used to reduce or eliminate pain and suffering that exists from typical leg movements.
As part of these surgical procedures, it has become common practice to secure the prosthesis to the bone or joint using a cement formed by mixing a polymer powder and a liquid monomer. The two components must be thoroughly blended together to achieve the required consistency for the fully mixed cement. The fully mixed cement is then loaded into a separate dispensing apparatus for placement in the desired area and affixing of the prosthesis to the desired site.
Other uses of bone cement include repairing or mending bone fractures or shattered bone occurring from extreme trauma. Bone cement may also be used during cosmetic or dental surgery. Moreover, bone cement may be used as a drug delivery or release system, whereby the bone cement is mixed with antibiotics or other desired drugs and applied to a specific surgical site such that the drugs leach out and are delivered directly to the surgical site. Some bone cements are also designed to be absorbed by the body over time.
Because of the necessity for a fairly quick setting material, the cement is almost universally prepared by a surgical assistant during the course of the operation in the sterile operating room. Conventional bone cements are generally polymeric materials which are prepared by copolymerization of the components as needed. Bone cement is prepared by copolymerizng the liquid monomer and the powdered copolymer, such as methyl methacrylate and polymethyl methacrylate or methyl methacrylate styrene. In order to provide a bone cement having the desired properties, the compounds must be uniformly and thoroughly mixed so that a homogeneous reaction product is produced.
During the mixing and subsequent chemical reaction various vapors are produced. Due to the noxious and toxic nature of such vapors, it is highly undesirable to be exposed to them, particularly for extended periods of time in the course of multiple preparations. Since it is necessary that the mixing be carried out for extended periods of time to ensure a uniform reaction product and a minimum of concentration of volatile reactants, the period of exposure to harmful vapors can be substantial. Moreover, during the mixing of the constituent components of the cement, air bubbles may be formed within the cement.
Most often, the two components forming the cement are mixed in a mixing vessel and, once fully mixed, the cement is manually transferred from the mixing vessel to a dispensing member of a dispensing device. Typically, devices similar to caulking guns are employed for dispensing the fully mixed cement to the desired location in the patient. These devices have a piston which allows the bone cement to remain in the dispensing member.
In some other prior art systems, the cement is mixed in one vessel which is then directly connected to a feeding system that enables the mixed cement to be added to a holding tube for use with the dispensing device. The dispensing system, however, is separate and exposes the mixed cement to the surrounding personnel. Furthermore, care must be exercised during the transfer of the mixed cement to the dispenser to avoid introducing air into the cement or to avoid dropping, spilling, or contaminating the cement.
Other prior art systems utilize a handle that operates mixing paddles in a closed cylinder for combining the cement constituents. Upon mixing the bone cement, the handle must be removed. Conventional systems incorporate frangible handles that when broken may produce fragments that could contaminate the bone cement.
One such device is disclosed in U.S. Pat. No. 5,551,778 to Hauke et al. The '778 patent discloses a device having a mixing cylinder and a mixing plunger extending therethrough. The standard powder and liquid components are introduced into the chamber to form a bone cement and the mixing plunger mixes the two components. The mixing plunger has a predetermined break point for breaking the mixing plunger and allowing for its removal from the mixing cylinder. A discharge nozzle is then connected to the mixing cylinder and the mixing chamber is connected to a drive mechanism. The drive mechanism includes a discharge plunger that is passed through the mixing cylinder forcing the bone cement from the mixing cylinder out the nozzle. A portion of the bone cement remains in the discharge nozzle and thus the system does not ensure complete delivery of the bone cement into the patient.
Another such device is disclosed in U.S. Pat. No. 5,879,116 to Barker et al. The '116 patent discloses a device having a mixing chamber integral with a delivery chamber. The bone cement components are introduced into the mixing chamber and a paddle having a handle extending from the mixing chamber is utilized to mix the components and form the bone cement. Once the components are adequately mixed, a passage way is opened between the mixing chamber and the delivery chamber. The handle is actuated causing rotation of the paddle and of an auger disposed within the delivery chamber. The paddle transfers the bone cement from the mixing chamber to the auger. The auger has threads, which taper away from the mixing chamber for pulling the bone cement from the mixing chamber into the delivery chamber. One disadvantage of this system is that the bone cement must have a relatively low viscosity to be pulled by the auger into the delivery chamber. Additionally, the bone cement may remain on the walls of the mixing chamber where the paddle is unable to reach it.
Accordingly, it would be advantageous to provide a bone cement mixing and delivery assembly that includes a mechanism to transfer all of the bone cement from a mixing chamber to an delivery cartridge and to deliver all of the bone cement from the delivery cartridge into the patient.